Standard characters can be a decent threat on their own. Where they fall short is, of course, how easy they are to kill. At least, at first glance.
The recommended encounter in terms of standards is one per character in the party. Include lieutenants and animal partners for this. If that adds up to five, Five standards will be worth one's XP value times the threat level.
What some may forget is... Do you have an entire party fighting off ONE critter or group of critters at a time? Those five standards are the same as one out-numbered special. They do have the advantage of multiple actions, but they could be going down rather quickly.
Seems to me the main solution is twofold. One, read up the NPC section a little more. Your health issues are answered by the health grade system (the scaling included), and the threat level of the campaign (most I run or am in run at TL+1).
Usually best to keep that to the heavily armored ones; and speaking of which, armor can be given to them fairly cheap. In fact, never buy DR for your NPCs, give them armor, give them extra health, give them resistances, but DR is too expensive compared to just buying a suit. Armor can come with various resistances by default too.
If you need them tougher still, there's always "tough", which lets them keep going after failing their save once (or more, but tough can be a very special beast to handle when you stack it).
Finally, don't forget that some parties can chew through a battle better than others. Once they get a bit of renown for their prowess, an opposing force of standards is either suicidal or a well organised (or just big) force. In the latter's case, we're looking at 2-3 full squads of standard character (probably 2 led by a special, or 3 alone), who are going to be focusing a very large number of rolls towards the party before attrition really sets in, so long as they didn't place themselves in perfectly fireballable formations when they knew the party had explosives or a caster.
At low threats this might be 10 archers supporting those 5 guards. When they know they're hunting a mid-high level, renowned war party? they'll bring out the bombards, scrolls and summons. A few hundred silver is a small price to pay for the bounty on THOSE heads, especially compared to the risks of taking them on more "normally".